Lesson 1

Getting to know your worms: Observing C. elegans

Driving Question: What does C. elegans look like, and how does it behave under laboratory conditions?

By the end of lesson one, we hope you will be able to:

Recall some basic information about nematodes
Explain why model organisms are useful in research
Identify the lifecycle stages of the model organism C. elegans

In this unit, we are going to change the environment for the nematode C. elegans and observe what happens. We will be observing two types of C. elegans: wild type and mutant. Wild type are the typical or "normal" strain. The mutant worms have a mutation in a gene that gives them different, or atypical, characteristics.

All living organisms are able to respond to changes in their environments.

The fur of the snowshoe hare can change color depending on the season. Reptiles may hibernate during the cold weather, and some birds lay their eggs earlier in the season in response to warmer weather. Dogs, cats, and coyotes can grow heavy fur in the fall and shed the extra fur in the spring.

How does this happen? As the environment changes, genes are regulated and expressed differently, leading to changes in the proteins made. One set of proteins may show up as brown fur, and other set as white fur.

While organisms can respond to the environment, their cells are performing a delicate balancing act that keeps the organism's functions within a healthy range. Feedback mechanisms maintain this balance, known as homeostasis.

In this unit, we will compare how the wild type and mutant worms differ when we move them from their normal environment ("low salt") to a challenging environment ("high salt").

What is C. elegans?

C. elegans is a nematode worm. Nematodes are the most abundant multi-cellular organisms in the world. They live everywhere--in soil or as parasites in plants, animals, or insects.

C. elegans:

Are about 1mm in length
Are not parasites
In the wild, they feed on bacteria from decomposing fruit or vegetation
In the lab, they feed on bacteria such as E. coli growing on agar plates

Reach sexual maturity at 3 days
Live up to 3 weeks
Have two sexes – hermaphrodites (XX) and males (XO)

(males are very rare in wildtype worm populations. Most are hermaphrodites.)

XX can self-fertilize or mate with males; but not each other

Watch the video to learn more.

Why C. elegans?

C. elegans is very well-known in the lab as a model organism.

Model organisms are living systems used to study biological processes. There are many types of models including plants, animals, and microbes.

Watch a segment of the video Meet the Nematode.

Be prepared to list three reasons why C. elegans is useful as a model organism.

Life cycle of C. elegans

C. elegans have three distinct life stages.

The egg (or embryo) stage
Four stages as larva (L1, L2, L3, L4)
Adult stage

How long does it take to grow from an egg to an adult?

See what the life stages look like on a plate in the lab.

N2 (written backwards on the plate) is the wild type worm strain.

Chill out and see how many life stages you recognize on your own. Become familiar with the normal movements of wild type worms in their preferred "low salt" environment. In the next lesson, you will compare this to a change in the environment.

Lesson One Comprehension Questions

A. List 4 things you learned about C. elegans.

B. Why do you think nematodes make a good model organism for understanding humans?

C. What are the life stages of C. elegans?

D. Approximately how long does it take to grow from an egg to an adult?

Next Step: Go to Lesson 2

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